The Moon and Venus

I have recently come across a new theory about the formation of the moon. It says that the Earth was rotating faster than it is now and was side-swiped by an object larger than Mars.
Is it possible that object was Venus and the collision caused the Earth to slow down and the rotation of Venus to be reversed thus explaining why Venus spins in the wrong direction.

Extremely unlikely. That would have resulted in an extremely elliptical orbit for Venus, which would have needed to be corrected in order for it to have the orbit we observe today. The chance that the combination of events required to make both of these things happen is very, very unlikely.